The sound transmission loss of a wall partition, ceiling, roofs or floor are determined by physical factors such as mass and stiffness. A complex interplay of factors works to prevent or allow the transmission of sound through surfaces. In a double layer assembly, such as plasterboard on wood or metal framing, the depth of air spaces, the presence or absence of sound absorbing material, and the degree of mechanical coupling between layers critically affect sound transmission losses.
The mass per unit area of a material is the most important factor in controlling the transmission of sound through the material. The so-called mass law is worth repeating here, as it applies to most materials at most frequencies:TL=20 log10(msf)−48.                where:                    TL=transmission loss (dB)            ms=mass per unit area (kg/m2)            f=frequency of the sound (Hz)                        
Stiffness of the material is another factor which influences TL. Stiffer materials exhibit “coincidence dips” which are not explained by the above mass law. The coincidence or critical frequency is shown by:fc=A/t                 where: A is a constant for a material                    t is the thickness of the material (mm)                        
There are other factors in wall, roof, ceiling & floor design such as the mass-air-mass resonance, which also affect transmission loss at different frequencies.
Generally, relying only on the mass law to achieve a specific TL results in a thick wall, ceiling or floor construction, which reduces usable floor area and ceiling height in an apartment dwelling. Attempts to avoid those coincidence dips noted above appear only to increase transmission loss slightly, if at all. Generally only very expensive and labour intensive solutions give an acceptable transmission loss. Building regulations are becoming more strict while more apartment blocks are being constructed, with cost being a pre-eminent factor.
The Sound Transmission Loss of a dividing structure separating two spaces varies with frequency. If the structure has a degree of stiffness, incident acoustic energy causes the structure to vibrate which re-radiates the acoustic energy on the other side of the structure. Low frequency re-radiation is mainly controlled by the structure stiffness. At about an octave above the lowest resonance frequency of the barrier, the mass of the structure takes over control of the re-radiation and dominates the sound reduction performance, and the mass law (above) indicates that doubling the mass of the structure increases the structure's noise attenuation performance by approximately 6 dB.
High frequency incident acoustic energy causes ripple-, or bending-waves of the surfaces of the structure. Unlike compression waves, the velocity of bending waves increases with frequency. Every ‘stiff panel construction’ has a critical or coincidence frequency which considerably reduces the Sound Transmission Loss of structural panel construction.
A common coincidence frequency occurs between 1000 & 4000 Hz and is caused by the bending wave speed in the material equaling the speed of sound in the medium surrounding the panel (in this case air). In this frequency range the waves coincide and reinforce each other in phase, greatly reducing the noise reduction performance of the panel at approximately the critical frequency.
The present invention seeks to ameliorate one or more of the abovementioned disadvantages of known methods of increasing TL such as higher cost, mass & reduced available space.
The present invention seeks to provide a construction partition panel laminate which improves acoustic transmission loss from one side to another.